The vomiting center in the brainstem contains high concentrations of substance P and its receptor, in addition to other neurotransmitters such as choline, histamine, dopamine, serotonin, and opioids. Their activation stimulates the vomiting reflex. Different emetic pathways exist, and substance P/NK1R appears to be within the final common pathway to regulate vomiting. 
Substance P antagonist (SPA) aprepitant is available in the market in the treatment of chemotherapy-induced nausea / emesis.
Substance P is involved in the transmission of pain impulses from peripheral receptors to the central nervous system. It has been theorized that it plays a part in fibromyalgia. Capsaicin has been shown to reduce the levels of Substance P probably by reducing the number of C-fibre nerves or causing these nerves to be more tolerant. Thus Capsaicin is clinically used as an analgesic and anti-inflammatory agent to relieve pain associated with arthritis and many types of neuralgia.
Stimulating cellular growth
Substance P has been shown to stimulate cellular growth in cell culture , and it was shown that Substance P could promote wound healing of non-healing ulcers in humans.  It has also been shown to reverse diabetes in mice. 
Naked mole rats lack Substance P and do not feel pain when painful stimuli are administered to the skin.
^ Hornby PJ. Central neurocircuitry associated with emesis. Am J Med 2001;111:106S-12S
^ Reid TW, Murphy C, Iwahashi C, Foster B, and Mannis M. Stimulation of epithelial cell growth by the neuropeptide substance P. J Cell Biochem 1993; 52:476-485
^ Brown S, Lamberts D, Reid TW, Nishida T, Murphy C. Neurophilic and Anhidrotric Keratopathy Treated with Substance P and Insulinlike Growth Factor 1. Arch Ophthalmol 1997; 115:926-927
^ Breakthrough sheds light on cause of diabetes - health - 15 December 2006 - New Scientist. Retrieved on 2007-05-08.
^ Steinitz H (1979). "[Chronic recurrent intestinal amebiasis in Israel (author's transl)]" (in German). Leber, Magen, Darm9 (4): 175-9. PMID 491812.
^ Stark D, van Hal S, Marriott D, Ellis J, Harkness J (2007). "Irritable bowel syndrome: a review on the role of intestinal protozoa and the importance of their detection and diagnosis". Int. J. Parasitol.37 (1): 11-20. doi:10.1016/j.ijpara.2006.09.009. PMID 17070814.
^ McGowan K, Kane A, Asarkof N, et al (1983). "Entamoeba histolytica causes intestinal secretion: role of serotonin". Science221 (4612): 762-4. PMID 6308760.
^ Park TJ, Comer C, Carol A, Lu Y, Hong HS, Rice FL (2003). "Somatosensory organization and behavior in naked mole-rats: II. Peripheral structures, innervation, and selective lack of neuropeptides associated with thermoregulation and pain". J Comp Neurol465 (1): 104–20. doi:10.1002/cne.10824. PMID 12926019.
^ Pepling, Rachel Sheremeta (January 7 2004). Ugly Ducklings. Chemical & Engineering News. Retrieved on 2007-08-14.